Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> writes: > On Fri, Sep 28, 2018 at 04:19:03PM +0800, Huang, Ying wrote: >> Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> writes: >> > One way is to change >> > copy_one_pte's return to int so we can just pass the error code back to >> > copy_pte_range so it knows whether to try adding the continuation. >> >> There may be even more problems. After add_swap_count_continuation(), >> copy_one_pte() will be retried, and the CPU may hang with dead loop. > > That's true, it would do that. > >> But before the changes in this patchset, the behavior is, >> __swap_duplicate() return an error that isn't -ENOMEM, such as -EEXIST. >> Then copy_one_pte() would thought the operation has been done >> successfully, and go to call set_pte_at(). This will cause the system >> state become inconsistent, and the system may panic or hang somewhere >> later. >> >> So per my understanding, if we thought page table corruption isn't a >> real problem (that is, __swap_duplicate() will never return e.g. -EEXIST >> if copied by copy_one_pte() indirectly), both the original and the new >> code should be OK. >> >> If we thought it is a real problem, we need to fix the original code and >> keep it fixed in the new code. Do you agree? > > Yes, if it was a real problem, which seems less and less the case the more I > stare at this. > >> There's several ways to fix the problem. But the page table shouldn't >> be corrupted in practice, unless there's some programming error. So I >> suggest to make it as simple as possible via adding, >> >> VM_BUG_ON(error != -ENOMEM); >> >> in swap_duplicate(). >> >> Do you agree? > > Yes, I'm ok with that, adding in -ENOTDIR along with it. Sure. I will do this. > The error handling in __swap_duplicate (before this series) still leaves > something to be desired IMHO. Why all the different returns when callers > ignore them or only specifically check for -ENOMEM or -EEXIST? Could maybe > stand a cleanup, but outside this series. Yes. Maybe. I guess you will work on this? Best Regards, Huang, Ying
